The abatement of emissions, particularly the oxides of nitrogen (NOx) is gaining increasing attention and significant resources are being applied to the associated problems.
It has been found that NOx is formed in the combustors of stationary gas turbines through two NOx forming mechanisms. Thermal NOx is formed by reaction between the nitrogen and oxygen in the air initiated by the high flame temperature and fuel NOx, on the other hand, results from the oxidation of organic nitrogen compounds in the fuel.
Various governmental agencies have proposed or enacted codes for regulating the NOx emissions of stationary gas turbines. For example, the United States Environmental Protection Agency has proposed a code limiting NOx emissions to 75 ppm at 15% oxygen with an efficiency correction. In Southern California, the Los Angeles County Air Pollution Control District's Los Angeles County Rule 67 limits NOx emissions to 140 lbs. per hour.
It has been found that the NOx emissions of a stationary gas turbine can be regulated by the addition of a suitable NOx suppressant fluid to the air supply of the gas turbine combustor. One example involves the recirculation of exhaust gases from a gas turbine-steam turbine combined power plant and is described in more detail in copending application Ser. No. 113,635, filed Jan. 21, 1980 of common assignee as the instant invention, the disclosure of which is hereby incorporated by reference. Another example involves the supply of an oxygen-deficient air mixture which is the by-product of an oxygen separation unit in a coal gasification plant, the oxygen being used together with coal to generate a medium BTU coal gas which is employed as the fuel for the stationary gas turbine combustor. The latter arrangement is described in more detail in copending application Ser. No. 113,637, filed Jan. 21, 1980 of common assignee as the instant invention, the disclosure of which is hereby incorporated by reference. Examples of other useful NOx suppressants in addition to the above are nitrogen, carbon dioxide and other high specific heat gases which are relatively inert.
When NOx suppressants are used, they are generally added to the air supply for the stationary gas turbine compressor. However, commercial gas turbines use a portion (15% or more) of the compressor discharge air for nozzle and turbine cooling. Since these air flows do not effect NOx emissions, adding the NOx suppressants to these flows represents a waste of the suppressant. Additionally, a minimum suppressant flow rate is desirable and concentrating a fixed amount of suppressant in only the combustor air or preferably in the primary reaction zone will produce better NOx control.